Port to oslo.messaging.Notifier API

Add a temporary nova.notifier.Notifier helper class which translates
oslo.messaging.Notifier compatible calls into openstack.common.notifier
compatible calls.

This allows us to port the notifier code over to the oslo.messaging API
before actually switching over oslo.messaging fully.

This patch contains no functional changes at all, except that all
notifications go through this temporary helper class.

Some notes on the new API:

  * The notifier API is changed so that what was previously global state
    is now encapsulated in a Notifier object. This object also includes
    the publisher_id and has error()/info()/etc. methods rather than
    just notify().

  * The notify_decorator() helper wasn't carried across to the new API
    because its semantics are a bit weird. Something along these lines
    could be added in future, though.

  * We use a fake Notifier implementation for tests because there's no
    API in oslo.messaging to actually get the notifications queued
    up in the fake notification driver, which is a bit dumb. However,
    this feels like the right thing to do anyway. We're not wanting
    to test oslo.messaging.Notifier itself, but rather we want to test
    how we call it.

blueprint: oslo-messaging
Change-Id: I262163c7e05e6a6fb79265e904ce761fc3ac5806

nova/compute/utils.py

@@ -27,10 +27,10 @@ from nova.compute import flavors
 from nova import exception
 from nova.network import model as network_model
 from nova import notifications
+from nova import notifier as notify
 from nova.objects import instance as instance_obj
 from nova.openstack.common.gettextutils import _
 from nova.openstack.common import log
-from nova.openstack.common.notifier import api as notifier_api
 from nova.openstack.common import timeutils
 from nova import utils
 from nova.virt import driver
@@ -191,12 +191,14 @@ def _get_unused_letter(used_letters):
     return letters[0]
 
 
-def notify_usage_exists(context, instance_ref, current_period=False,
+def notify_usage_exists(notifier, context, instance_ref, current_period=False,
                         ignore_missing_network_data=True,
                         system_metadata=None, extra_usage_info=None):
     """Generates 'exists' notification for an instance for usage auditing
     purposes.
 
+    :param notifier: a messaging.Notifier
+
     :param current_period: if True, this will generate a usage for the
         current usage period; if False, this will generate a usage for the
         previous audit period.
@@ -228,29 +230,24 @@ def notify_usage_exists(context, instance_ref, current_period=False,
     if extra_usage_info:
         extra_info.update(extra_usage_info)
 
-    notify_about_instance_usage(context, instance_ref, 'exists',
+    notify_about_instance_usage(notifier, context, instance_ref, 'exists',
             system_metadata=system_metadata, extra_usage_info=extra_info)
 
 
-def notify_about_instance_usage(context, instance, event_suffix,
+def notify_about_instance_usage(notifier, context, instance, event_suffix,
                                 network_info=None, system_metadata=None,
-                                extra_usage_info=None, host=None):
+                                extra_usage_info=None):
     """
     Send a notification about an instance.
 
+    :param notifier: a messaging.Notifier
     :param event_suffix: Event type like "delete.start" or "exists"
     :param network_info: Networking information, if provided.
     :param system_metadata: system_metadata DB entries for the instance,
         if provided.
     :param extra_usage_info: Dictionary containing extra values to add or
         override in the notification.
-    :param host: Compute host for the instance, if specified.  Default is
-        CONF.host
     """
-
-    if not host:
-        host = CONF.host
-
     if not extra_usage_info:
         extra_usage_info = {}
 
@@ -258,13 +255,11 @@ def notify_about_instance_usage(context, instance, event_suffix,
             network_info, system_metadata, **extra_usage_info)
 
     if event_suffix.endswith("error"):
-        level = notifier_api.ERROR
+        method = notifier.error
     else:
-        level = notifier_api.INFO
+        method = notifier.info
 
-    notifier_api.notify(context, 'compute.%s' % host,
-                        'compute.instance.%s' % event_suffix, level,
-                        usage_info)
+    method(context, 'compute.instance.%s' % event_suffix, usage_info)
 
 
 def notify_about_aggregate_update(context, event_suffix, aggregate_payload):
@@ -282,9 +277,10 @@ def notify_about_aggregate_update(context, event_suffix, aggregate_payload):
                         "notification and it will be ignored"))
             return
 
-    notifier_api.notify(context, 'aggregate.%s' % aggregate_identifier,
-                        'aggregate.%s' % event_suffix, notifier_api.INFO,
-                        aggregate_payload)
+    notifier = notify.get_notifier(service='aggregate',
+                                   host=aggregate_identifier)
+
+    notifier.info(context, 'aggregate.%s' % event_suffix, aggregate_payload)
 
 
 def get_nw_info_for_instance(instance):